5. Hot filtration by using the known weight filter paper (from step No.1) and then rinse
with hot water until no acid is detected by pH paper.
6. Transfer the residual on the filter paper to an original one 500 ml beaker or duran
bottle.
7. Add 200 ml of 1.25% sodium hydroxide and then boil in the hot plate or water baht for
30 min. Cover the beaker with foil or loose cap duran bottle.
8. Hot filtration by using the original one filter paper (from step No.5) and then rinse with
hot water until no base is detected by pH paper.
9. Rinse with 20 ml of ethyl alcohol (95%)
10. Dry the filter paper contained the residue in hot air oven (105o
C) for 3 h and cool in
desiccators, then record the weight.
11. Put the dried filter paper contained the residue in known weight crucible (from step
No.2) and then incinerate in the furnace as the same method used for ash content determination.